This invention relates to a vacuum-control modulator arrangement for an automatic transmission of a motor vehicle, primarily for use in conjunction with a diesel or other fuel-injection engine.
An automatic transmission of the motor vehicle must bring the gearshift operations into harmony with the torque thereto, i.e., the torque of the engine, regardless of the types of engines. Otherwise, the correct gear-change actions could not take place at the correct moment, which could result in an increase of the shock associated with gear-change actions. Thus, the gearshift operations may be worsened to the point of driving discomfort.
In carburetor type engines, as the vacuum at the induction manifold is substantially proportionate to the engine torque, the control oil pressure (throttle pressure) corresponding to the induction manifold vacuum is usually produced to control the gearshift operations thereby.
However, in fuel injection type engines such as diesel engines, because the induction manifold vacuum is not proportionate to the engine torque, it cannot be used as a source of transmission control.
FIG. 1 shows a prior art vacuum modulator arrangement for an automatic transmission which is disclosed in U.S. Pat. No. 3,738,197 to K. Brumm et al. A vacuum pump 10 is connected via a line 11 at a branch portion 12 to two parts: a brake power booster 14 of a diesel-driven motor vehicle through a non-return valve 13; and a vacuum modulator 16 through a line 15 which modulator 16 is positioned near a fuel-injection pump 17 at the opposite side of an engine 20'. By actuating the vacuum modulator 16 in response to the fuel-injection pump 17, the vacuum from the vacuum pump 10 is controlled and transmitted via the line 18 to the throttle modulator 19 where the throttle oil modulating operations for the gearshift actions of the automatic transmission take place in a well known manner.
The vacuum modulator 16 is designed so that the effective areas of communication between the lines 15 and 18 and between the line 18 and the opening (not shown) to the atmosphere can be controlled to produce a proper vacuum into the line 18. Thus, in the prior art arrangement, the line 15 between the branch portion 12 and the vacuum modulator 16 must be long. Also, the line 18 between the throttle modulator 19 and the vacuum modulator 16 must be long. In practice, such lines are complicated. As a result, the production costs thereof are high. As the vacuum modulator 16 is to simultaneously change or control the effective areas between the two pair of lines, only one throttle characteristic of the vacuum modulator can be obtained. When the accelerator is completely closed, the output vacuum is the same as the pressure of the vacuum source, and when it is completely open, it is the same as the atmospheric pressure.
A thin slit is used as a throttle means. For such a reason, some structural defects such as dust clogging or the like cannot be avoided.